Abstract

A class of experiments aimed at observing quantum features in the macroscopic domain has been discussed in the last decade.1,2 They are all based on the repeated monitoring of some observable of an unique macroscopic system which can be alternatively described by quantum mechanics or by realistic theories. These last are theories for which we assume, as in classical physics, that an observable has a defined value even if it is not observed. Be11-type inequalities have been written for such systems which should be violated by the experimental data if quantum mechanics holds, as in the case of the spatial Bell inequalities already known and well experimentally tested against local realism. However, unlike the case of these last, where correlation probabilities between each pair of photons are measurable, to test macrorealism one must have a single system subjected to repeated measurements. For instance, an rf-SQUID has been suggested as a system in which repeated measurements of magnetic flux can be performed.’ 1 lie effect of the previous measurements on the next outcome cannot be neglected and has to be taken into account in the dynamics. The effect of the measurement can be included through a filtering operator which acts on the state undergoing the measurement and projects it on the eigenstates which are closest, to the eigenvalue obtained in the measurement.